S WITCHING SURGE design criteria, developed from
the results of miniature system studies of the Allegheny
Power System (APS) 500-kV system, coupled with contamination
considerations, dictated the tower-insulation
design requirements: 1) twenty-four 53/4 X 10-inch suspension
insulators in V-string configuration, 2) a minimum
strike to the tower side of 11 feet 2 inches, and 3) a minimum
vertical strike to the tower top of 12 feet 10 inches. These
requirements were obtained from simulated tower--insulation
test results as presented in a recent technical paper [1].
Although several investigations have been performed on
simulated tower-insulation systems [1]- [8], only a few
studies have reported test results on the full-scale tower
insulation [1], [3], [9 ]. Therefore, it was deemed necessary
to test the APS 500-kV tower-insulation system not only to
prove the adequacy of the switching surge design, but also
to determine the impulse time-lag curves and the 60-cycle
strength. The switching surge insulation strength was investigated
for both positive and negative polarity, wet
and dry, for the center and outside phase. Because of the
test requirements set forth for these verification tests, the
accuracy of the data was greatly improved, and additional
information was obtained on the nature of the switching
surge flashover probability curve.